1. Field of the Invention
The present invention relates to a dielectric ceramic composition suitable to the material for dielectric resonators, etc. In particular, the invention relates to a dielectric ceramic composition, which has a relative dielectric constant xcex5r of from 10 to 50 or so, which can be sintered at low temperatures, and which has a large unloaded Q value and has a small absolute value of a temperature coefficient of resonant frequency (xcfx84f).
2. Description of the Related Art
With the recent tendency in the art toward highly integrated microwave circuits, desired are small-sized high-performance dielectric resonators for them. The requirements of dielectric ceramic compositions for such dielectric resonators are that their relative dielectric constant xcex5r is relatively large, their unloaded Q is large and their temperature coefficient xcfx84f of resonant frequency is small. In general, resonators can be more small-sized with the increase in the relative dielectric constant xcex5r of the material for them. However, with the increase in their resonant frequency, resonators are more small-sized. Therefore, in order that resonators are not too much small-sized, the relative dielectric constant xcex5r of the material for them is desired to fall within a suitable range depending on the use of resonators. The present invention relates to a dielectric ceramic composition having a relative dielectric constant xcex5r of from 10 to 50 or so.
For such dielectric ceramic compositions, proposed are a dielectric ceramic composition of BaOxe2x80x94TiO2xe2x80x94Nd2O3 [Ber. Dt. Keram. Ges., 55 (1978), Nr. 7; Japanese Patent Laid-Open No. 35406/1985] and a dielectric ceramic composition of BaOxe2x80x94TiO2xe2x80x94Nd2O3xe2x80x94Bi2O3 [Japanese Patent laid-Open No. 72558/1987].
These days disclosed are stacked chip capacitors and stacked dielectric resonators formed of dielectric ceramic composition layers, for which the ceramic composition and the internal electrode are baked simultaneously to give a stacked structure. However, since the temperature at which the dielectric ceramic composition is baked is high, generally falling between 1300 and 1400xc2x0 C., the composition is often difficult to bake simultaneously with the inner electrode. For this reason, the electrode material for the stacked structure is limited to palladium (Pd), platinum (Pt) and the like that are still stable even at high temperatures. Given that situation, desired in the art are dielectric ceramic compositions that can be combined with any other inexpensive electrode material such as silver (Ag), silver-palladium (Agxe2x80x94Pd) or copper (Cu) so as to be baked simultaneously with it even at low temperatures not higher than 1200xc2x0 C. On the other hand, with the recent tendency in the art toward increased channel capacity, the frequency in communication is being shifted to a high frequency region of 2 GHz or more. With that, the dielectric material in the art is now required to have a relative dielectric constant of from 10 to 50 or so.
Regarding the material, Japanese Patent Laid-Open No. 211564/1994 discloses a ceramic substrate prepared by mixing a dielectric ceramic composition of BaOxe2x80x94TiO2xe2x80x94Nd2O3 with a specific glass component followed by baking it; and Japanese Patent Laid-Open No. 40767/1994 discloses a method for producing a dielectric ceramic composition like the mixture capable of being baked even at low temperatures. However, the relative dielectric constant of the dielectric ceramic compositions disclosed in these laid-open patent publications is relatively large, generally falling between 70 and 80 on average, and is therefore unsuitable to use thereof in a high frequency region. Regarding the unloaded Q of these compositions, the fQ value thereof which is a product of Q and the resonant frequency thereof is low, generally falling between 1000 and 3000 GHz or so on average. Therefore desired are dielectric ceramic compositions having a larger unloaded Q. Another important factor of dielectric ceramic compositions is that their characteristics are stable independent of varying ambient temperatures. However, the temperature-dependent capacitance of the dielectric ceramic compositions heretofore disclosed as above fluctuates in a broad range falling between xe2x88x9270 and 40 ppm/xc2x0 C.
One object of the present invention is to provide a dielectric ceramic composition having good properties suitable to the material for dielectric resonators, especially to provide such a dielectric ceramic composition, of which the dielectric constant falls between 10 and 50 or so, preferably between 10 and 30 or so, the unloaded Q is large and the temperature-dependent resonant frequency change is small, and which can be sintered well even when baked at low temperatures.
In its first aspect, the invention provides a dielectric ceramic composition including as an essential component a composition represented by the formula of xBaO-yTiO2-zNd2O3, wherein 0.02xe2x89xa6xxe2x89xa60.2, 0.6xe2x89xa6yxe2x89xa60.8, 0.01xe2x89xa6zxe2x89xa60.3, x+y+z=1, with the ceramic composition further comprising:
a first glass component comprising PbO, ZnO and B2O3;
a second glass component comprising SiO2 and B2O3, with the first and second component having the following relationship 10xe2x89xa6axe2x89xa680 and 1xe2x89xa6bxe2x89xa6100 wherein xe2x80x9caxe2x80x9d indicates the content of the first glass component and xe2x80x9cbxe2x80x9d indicates the content of the second glass component with both xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d in parts by weight relative to 100 parts by weight of the essential component; and
a third component comprising Al2O3, SrTiO3, GeO2 and Li2O with the content of each such compound to be determined from the following: 1xe2x89xa6cxe2x89xa660, 0.1xe2x89xa6dxe2x89xa630, 5xe2x89xa6exe2x89xa630 and 0.1xe2x89xa6fxe2x89xa67, wherein xe2x80x9ccxe2x80x9d indicates the content of Al2O3, xe2x80x9cdxe2x80x9d indicates the content of SrTiO3, xe2x80x9cexe2x80x9d indicates the content of GeO2 and xe2x80x9cfxe2x80x9d indicates the content of Li2O all in parts by weight relative to 100 parts by weight of the essential component.
In its second aspect, the invention provides a dielectric ceramic composition including as all essential component a composition represented by the formula of s(xBaO-yTiO2-zNd2O3)-tNd2Ti2O7, wherein 0.02xe2x89xa6xxe2x89xa60.2, 0.6xe2x89xa6yxe2x89xa60.8, 0.01xe2x89xa6zxe2x89xa60.3, x+y+z=1, 0.1xe2x89xa6sxe2x89xa60.8, 0.2xe2x89xa6txe2x89xa60.9, s+t=1, with the ceramic composition further comprising:
a first glass component comprising PbO, ZnO and B2O3;
a second glass component comprising SiO2 and B2O3, with the first and second component having the following relationship 10xe2x89xa6axe2x89xa680 and 1xe2x89xa6bxe2x89xa6100 wherein xe2x80x9caxe2x80x9d indicates the content of the first glass component and xe2x80x9cbxe2x80x9d indicates the content of the second glass component with both xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d in parts by weight relative to 100 parts by weight of the essential component; and
a third component comprising Al2O3, SrTiO3, GeO2 and Li2O with the content of each such compound to be determined from the following: 1xe2x89xa6cxe2x89xa660, 0.1xe2x89xa6dxe2x89xa630, 5xe2x89xa6exe2x89xa630 and 0.1xe2x89xa6fxe2x89xa67, wherein xe2x80x9ccxe2x80x9d indicates the content of Al2O3, xe2x80x9cdxe2x80x9d indicates the content of SrTiO3, xe2x80x9cexe2x80x9d indicates the content of GeO2 and xe2x80x9cfxe2x80x9d indicates the content of Li2O all in parts by weight relative to 100 parts by weight of the essential component.
The invention also provides a method for producing the dielectric ceramic composition of the second aspect as above, comprising the step of mixing a calcined powder of xBaO-yTiO2-zNd2O3, wherein 0.02xe2x89xa6xxe2x89xa60.2, 0.6xe2x89xa6yxe2x89xa60.8, 0.01xe2x89xa6zxe2x89xa60.3, x+y+z=1 and a calcined powder of Nd2Ti2O7 in a predetermined ratio and baking the mixed powders.
The advantages of the dielectric ceramic composition which the invention provides herein are that its dielectric constant falls between 10 and 50 or so, preferably between 10 and 30 or so, its unloaded Q is at least 3000 GHz in terms of its fQ value and is large, and its temperature coefficient xcfx84f of resonant frequency does not fluctuate but is stable, falling between xe2x88x9215 and 12 ppm/xc2x0 C. In addition, the dielectric ceramic composition of the invention can be sintered at low temperatures, and can form layers along with an internal electrode of Ag, Agxe2x80x94Pd, Cu or the like.